Paul was a United player for seven years but left the club, aged 23, having made one Carling Cup appearance - and has quit the game at 29.
Canaries defender Tierney said: "I was a United fan and had posters of Eric Cantona, Roy Keane and Mark Hughes.
"I saw the club inside and saw the great professionalism of Giggs and Scholes. But once my brother left, the view of United was tarnished as I wanted him to do so well.
"They still have fantastic players and a great manager but we are hoping to go there and get something.
"My brother is not playing any more as he became disillusioned with the game.
"I've watched a lot of games and always imagined what it would be like walking out at Old Trafford."